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Backbone A------------------Backbone B
Metro network equipment NE5KE and provincial backbone network equipment interconnected through EBGP. The NE5KEs in the metro network advertised routes to each other using OSPF, an IGP type, and advertised routes to the backbone networks using BGP.Symptom: After services were migrated to NE5KE-A, some users complained that their E-Line services were faulty and Internet access speed was slow.
Possible causes include:
1. The forwarding performance of NE5KEs degraded.
2. Certain links did not work properly.
3. Routing problems existed.
Huawei completed the following steps to diagnose the problem:
1. Checked FIB table entries at the software level and hardware level. No exception existed
2. Queried port data. Error packets did not increase. Ping tests indicated that links were available.
3. Checked whether NE5KE-A learned service routes within the metro network.
NE5KE-A learned the routes of the service network segment (XXX.YY.24.0/23) connected to SRs. The routes were OSPF ASE routes and egress port g2/0/8 was toward the SRs.
<A>dis ip ro XXX.YY.24.0
Routing Table : Public
Summary Count : 1
Destination/Mask Proto Pre Cost NextHop Interface
XXX.YY.24.0/23 O_ASE 70 21 WWW.ZZZ.251.10 GigabitEthernet2/0/8
4. Checked the service network segment of the metro network advertised from NE5KE-A to the backbone network.
Service network segment XXX.YY.24.0/22 was advertised over a blackhole route with a 22-bit mask through BGP.
ip route-static XXX.YY.24.0 255.255.252.0 NULL0 preference 210----The preference value of the blackhole route was 210.
preference 20 80 80
network XXX.YY.24.0 255.255.252.0-----The network segment advertised by the BGP network had a 22-bit mask.
5. Checked how the NE5KE-A (NE A) and NE5KE-B (NE B) imported static routes.
They imported all static routes through OSPF.
ospf 163 router-id y.y.y.y
default-route-advertise cost 1 type 1
import-route direct cost 0 type 1
import-route static type 1-----No filtering policy was set for importing static routes.
preference ase 70----The preference value of OSPF ASE routes was 70.
6. Checked the service route XXX.YY.24.0, which had a 22-bit mask, on NE A and NE B. Route flapping occurred, with the blackhole route, OSPF ASE route, and IBGP route alternately selected.Preference value of varied routes:
1. Set the preference value to 50 for static routes and to 150 for OSPF ASE routes.2. It is recommended to modify the OSPF route import policy, so the static blackhole route is not imported.